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Forums > C64 Coding > m.l. keyboard scan - WinVice or Basic behavior?

2015-02-13 11:26

mstram
Account closed

Registered: Dec 2013
Posts: 112

m.l. keyboard scan - WinVice or Basic behavior?

If I run this directly from the vice monitor, (g 812) it works as expected : useless screen flashing until any key pressed.

If I run it from BASIC (sys 2066), it returns immediately, without any keys pressed (updates screen only once), until I added the "flush" code (my guess at what the problem was).

I.e. SYS 2066 doesn't work, SYS 2061 does.

; *=$80D / 2061
; jmp r1

; -------- BASIC "flush" code --------
r1
jsr keyscan
bne r1
; ---------------------------------------
; $812 / 2066

SEI
l1 INC $d021 ; screen bk color
jsr keyscan
beq l1
CLI
RTS

keyscan
LDA #$00
STA $DC00 ; test keyboard for any key pressed
LDA $DC01
CMP #$FF ; no key
rts

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2015-02-14 14:07

chatGPZ

Registered: Dec 2001
Posts: 11386

Quote:

Gpz you are right: the "key" need to be debounced...

this has nothing to do with "debounce" actually. its as simple as that if you want to distinguish between two seperated keypresses, you have to wait for the first keypress to be over before you can check the next.

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